Year of Publication


Degree Name

Master of Science (MS)

Document Type

Master's Thesis


Agriculture, Food and Environment



First Advisor

Dr. Jennifer White


Introduced species, like the lady beetle Harmonia axyridis, have been linked to declines of native species through mechanisms including intraguild predation and competitive superiority. However, competitive differentials between species may be mitigated if subdominant species can utilize resources that dominant species cannot. Previous research has shown that some strains of the aphid Aphis craccivora are toxic to H. axyridis. My goal was to investigate use of this resource by both H. axyridis and other lady beetles, to determine whether these aphids might be an exploitable resource for subdominant lady beetle species. I first examined the behavioral responses of adult and larval H. axyridis to toxic strains of A. craccivora. I found that adults invested less time and laid fewer eggs with toxic than nontoxic aphids, and larvae consumed toxic aphids at a slower rate, often refusing them as a food source. I then tested whether six other lady beetle species could use the aphids, monitoring larval development in no-choice environments with different strains of A. craccivora. All species showed increased survival and development rates relative to H. axyridis on toxic aphid strains, suggesting these aphids may allow other coccinellid species to experience competitive release from the otherwise dominant H. axyridis.

Digital Object Identifier (DOI)